1. Field of the Invention
The invention relates to optical systems such as zoom viewfinder systems.
2. Description Relative to the Prior Art
Cameras using zoom lens systems are well known. In such cameras viewing of the scene by the operator is facilitated by providing a viewfinding device, i e., a viewfinder that allows the operator to view the object whose image is being recorded by the camera. In those cameras providing through the lens reflex viewing, the image of the object is viewed immediately prior to exposure by using a mirror which is moved before exposure of the film. Camera cost savings may be realized by eliminating the reflex viewing system. However, a need arises to provide a viewing system separate from the exposing system and to have said viewing system be provided with the ability to continuously vary the angular field of view, popularly referred to as zooming. Heretofore, zoom viewfinders of the Galillean type have been suggested. However, because zoom viewfinders of the Galillean type become increasingly large and complex when designed to the 2:1 and greater variable power range and because they have a poorly delineated field of view, other known systems consisting of a zooming objective as the first portion followed by an eyepiece have been developed. While these other systems can be designed for large variable power ranges, they also can become large and complex because of the need for an erecting means. Other systems also employ a field mask to delineate the boundaries of the field of view. This field mask is fixed at the image plane location and is located at the front focal plane of the eye lens element. The field mask is embodied as a clear opening in a thin opaque material. This type of a fixed or stationary field mask is not acceptable for use in an optical system having a drifting image plane. While a movable field mask may be provided, additional means is required to move same thereby adding complexity to such systems.